1. Field of Invention
This invention relates to the art of applying coatings to a series of workpieces, and more particularly to a continuous process for fusing a metal coating to a series of metal workpieces, and most particularly to a continuous process for applying a metal coating to a series of metal workpieces and passing the coated workpieces through induction coils to create a fused layer in the outer surface of the workpieces.
2. Description of Related Art
It is often advantageous to provide a coating over the outer surface of an item in order to improve its appearance or performance. For example, automobile bumpers are often coated with a layer of chrome to improve appearance and prevent oxidation. Certain workpieces made of iron are often coated with zinc in order to improve their resistance to oxidation. While the coating of iron workpieces with zinc is well-known, manufacturing difficulties are presented when structural steel shapes, such as channels and angles, are coated with zinc. Conventional methods of coating such large structural steel shapes include "hot-dip" or electrolytic galvanizing. The conventional process requires the repetitive dipping of the entire section or workpiece into large tanks of caustic soda, sulfuric acid, water, and molten zinc. This conventional process essentially achieves only a surface coating with a limited fusion of the zinc into the surface of the structural steel. Finally, the recent numerous governmental pollution control regulations on the electroplating industry require large investments in pollution control equipment to assure compliance.
Hot-dip galvanized zinc coatings have a slight surface degree of alloying reaction compared to the instant invention. The shallow layer of coating is 100% zinc on the surface and, in the best case, a maximum of 75% zinc and 25% iron at the substrate interface. However, in the inventive process herein described, the sprayed metal coating, such as zinc, will be subjected to an alloying process causing the zinc to fuse deeply into the substrate. This gives a uniform zinc-iron alloy to preselected depths. Hotdip galvanizing is dependent almost entirely on the surface thickness of the zinc coating, which is vulnerable compared with a deeply fused layer of alloy. By means of induction heating, a high percentage of heat is generated at the non-ferrous interface, promoting a diffusion not possible in a dipped procedure.
U.S. Pat. No. 2,414,923 to Batcheller discloses a method of coating a metal surface with a second metal by using spray guns which melt a coating metal supplied to the guns in the form of wire. U.K. Patent Application No. GB 2 210 064 A discloses a process for coating a substrate which comprises applying a layer of self-flowing metal-based alloy by thermal spraying and subjecting at least a zone in the layer to inductive heating.
Although these other processes may be technically feasible, they can be commercially unattractive due to cost. It is believed that the present invention will be of lower cost due to its lack of environmental disposal problems as well as the high tonnages capable through the process. Ultimate production rates will be established by operation and calibration, but tonnages greater than hot-dip galvanizing can be achieved at lower cost due the continuous nature of the line. Each of these variables can be controlled by a programmable logic controller, thereby contributing to the continuous nature of the process.
The present invention contemplates an new and improved process which is less expensive, provides a superior product, and does so in a more environmentally safe manner.